1. Field of the Invention
This invention pertains to an injection control device for a fuel injection pump of a diesel engine, and more specifically, to a device that controls an injection level by use of a solenoid valve installed between the high-pressure side and the low-pressure side of the pump.
2. Description of the Related Art
It is well known that there is a conventional injection control device wherein a solenoid valve is installed between the high-pressure side leading to the compressor and the low-pressure side leading to the fuel-intake in the fuel injection pump, and in which the high-pressure side and the low-pressure side are connected while fuel-intake is in progress to introduce the fuel into the compressor from the low-pressure side, whereas the connection between the high-pressure side and the low-pressure side is cut off while compression is in progress, to inject the fuel from the compressor.
This type of injection control device, whose further development is now being worked on by the applicant, has a system wherein a valve body of the solenoid valve and an armature coacting with the valve body are connected; a spill chamber for allowing the high-pressure fuel to leak is formed around the valve head; an armature chamber for accommodating the armature is formed around the armature; and inside or around the valve body, a passage connecting the spill chamber and the armature chamber is formed, maintaining the pressure balance between the spill chamber and the armature chamber.
In the aforementioned technology, however, because the fuel spilled from the high-pressure side has very high pressure as high as 1500 kg/cm.sub.2, periodic high-pressure surges in spike form are transferred from the spill chamber to the armature chamber via the aforementioned connection passage, by the fuel momentarily leaked to the low-pressure side when the solenoid valve has been opened, circulating around the armature, and colliding with the solenoid surface. After some period of time, this may possibly cause corrosion or deformation of a resin material covering the stator or coil, as shown in FIG. 6.
The valve body constituting the solenoid valve is constructed of different members at the front and the rear of the valve seat, which are inserted into the valve housing, and a sliding unit (i.e. opposed sliding surfaces) is formed in the area where the insertion is made. Although there is some clearance in each sliding unit (i.e. between sliding surfaces), there are cases when the centers of the holes in which the valves slide do not necessarily agree (i.e. the holes may be misaligned), at the front and the rear of the valve seat, since the valve body moves in only the axial direction. This may be due to an error in selecting the size of each constituent member of the solenoid valve, or an error in assembling these members. If, in this case, the gap between the hole centers (i.e. the amount of misalignment) is within (or less than) the amount of the clearance between sliding surfaces, there will be no problem. But, if the gap exceeds the amount of clearance, this can possibly prevent the smooth movement of the valve body.
To solve this problem, it can be considered that accuracy in assembling the valve constituent members should be improved to limit the gap between the hole centers within the amount of clearance, but this will require some means to assure accuracy in assembling and additional procedures.